clarify keyed v-for rule in SG

Author: chrisvfritz

src/v2/style-guide/index.md

@@ -244,7 +244,7 @@ props: {
 
 **Always use `key` with `v-for`.**
 
-It's _always_ required on components, in order to maintain internal component state down the subtree. Even for elements though, it's a good practice to maintain predictable behavior, such as [object constancy](https://bost.ocks.org/mike/constancy/) in animations.
+`key` with `v-for` is _always_ required on components, in order to maintain internal component state down the subtree. Even for elements though, it's a good practice to maintain predictable behavior, such as [object constancy](https://bost.ocks.org/mike/constancy/) in animations.
 
 {% raw %}
 <details>